1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device having a CMOS structure or a BiCMOS (Bipolar-CMOS) structure in which a capacitor is formed.
2. Description of the Background Art
In manufacturing processes of a semiconductor device having a CMOS or a BiMCOS structure, capacitative elements are often formed therein, and nitride film capacitors and MOS capacitors, which have a nitride film such as an ONO film and an ON film formed into a capacitative structure, are usually used.
However, since the MOS capacitor has the following characteristics, it is difficult to increase its capacitance value per unit area and to improve its voltage dependency.
(1) Since a gate oxide film is used as a dielectric film of a capacitor, the electrical characteristics such as a capacitance value per unit area is determined by the gate oxide film.
(2) The gate oxide film forming a dielectric film is generally made from a thermal oxide film, with the result that its capacitance value per unit area is smaller than that of a nitride film capacitor.
(3) Since a depletion layer extends from a source-drain region, the voltage dependency of the capacitor is extremely strong, and in order to prevent this, a diffusion region having a high concentration of impurities needs to be preliminarily formed, and when the concentration of impurities in the well region becomes too high, it is oxidized at higher speeds, and the capacitance value per unit area becomes smaller.
On the other hand, in the case of the application of a nitride film capacitor, since it is necessary to fabricate a formation layer exclusively used for the capacitor, the number of masks to be used increases, causing an increase in the manufacturing period and manufacturing costs.
It is an object of the present invention to provide a semiconductor device which makes it possible to increase a capacitance value per unit area while reducing the manufacturing costs to the minimum required and which has a capacitor that is free from voltage dependency, and a manufacturing method thereof.
The present invention is intended for a manufacturing method of a semiconductor device including a capacitor and insulating gate-type transistors formed in a predetermined base substrate. According to the third aspect of the present invention, the method includes the following steps (a) to (e). The step (a) is prepare a predetermined base substrate having a first area for forming a capacitor and a second area for forming an insulating gate type transistor. The step (b) is to successively deposit a lower-layer electrode-use conductive layer and a dielectric-use insulating film on the predetermined base substrate. The step (c) is to pattern the lower-layer electrode-use conductive layer and the dielectric-use insulating film to form a lower-layer electrode and a dielectric film of the capacitor by using a lower-layer electrode-use mask. The step (d), which is performed after the step (c), is to form an upper-layer electrode-use conductive layer on the predetermined substrate including the first and second areas. The step (e) is to perform a patterning process on the upper-layer electrode-use conductive layer by using an upper-layer electrode-use mask to form an upper-layer electrode of the capacitor in the first area and a gate electrode of the insulating gate type transistor in the second area.
Since, at the step (c), the lower-layer electrode-use conductive layer and the dielectric-use insulating film are patterned to form a lower-layer electrode and a dielectric film of the capacitor by using a lower-layer electrode-use mask, it is only necessary to add one sheet of mask of step (c) so as to pattern the lower-layer electrode and the dielectric film in comparison with conventional manufacturing methods of insulating gate-type transistors.
In addition, at step (e) that is independent of step (c), the upper-layer electrode and the gate electrode of the insulating gate-type transistor are simultaneously formed so that, at this step (e), the gate insulating film below the gate electrode is also formed; thus, the dielectric film of the capacitor and the gate insulating film of the insulating gate-type transistor are respectively formed in an independent manner at step (c) and step (e).
Therefore, since the film thickness, film quality and material of the dielectric film can be altered freely, it is possible to set the capacitance value per unit area to a desired value. Moreover, the structure of the above-mentioned capacitor makes it possible to prevent voltage dependency caused in MOS capacitor.
As a result, it becomes possible to obtain a semiconductor device which increases a capacitance value per unit area while reducing the manufacturing costs to the minimum required, and is free from voltage dependency.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.